It's time to talk a little bit about the goals of this project. On the face of it, there is really very little creativity in it: it's basically just a carrier PCB for the Circuit Playground Express board, with a battery, charger and some connectors. You can build three projects like that before breakfast. There is absolutely nothing novel or revolutionary or technically challenging in here.
On the other hand, I am not aware of anything like this already existing, and I am convinced that and existence of something like this would be extremely useful for a lot of people. Not just for beginners, who are afraid to try soldering, or designing a PCB like this, but also experienced wearable builders and cosplayers, who don't need to reinvent the wheel every time, and can simply build their stuff around an already existing design.
If you look at, say, Arduino, it wasn't a "revolutionary" project either. Every single thing on it has been done before multiple times and was widely available. But Arduino made it easier for everyone by bringing those things together in one package, and creating a standard platform to build on, sharing and re-mixing your designs.
A bare microcontroller board lets you build anything — the possibilities are infinite, and mind staggers confronted with a blank page. A base like the Barrette Hub limits your freedom and suggests what to build — making it much easier to begin, and hopefully bringing more people into the wonderful world of interactive wearables. Later on, when you are more experienced, you can leave it for other, more flexible and universal solutions, but you will probably still come back when your particular use case is a good fit, and a ready solution can save you time.
Will it work? Will the platform become popular? Will the idea catch on? Will it become an actual standard? I have no idea, this is very much a question of luck and of appearing at just the right time and place. I believe the right time for this kind of platform is closing in fast, and I am willing to do the work to give it a try. Time will tell if it's a wasted effort or not, but in the worst case I still learn a lot in the process.